We have discovered an inducible and morphologically indistinguishable bacteriophage in several Streptococcal strains that have previously been shown to induce caries in experimental animals. We seek to elucidate the role of the phage in determining the cariogenic properties of the bacteria. This will be accomplished by a) curing cariogenic bacteria of their prophage followed by a determination of their ability to induce dental caries in correlative studies. We are using a method of curing cells that involves inducing mutation to temperature inducibility of the lysogen. This enables us to readily cure cells and identify and select for the cured derivatives as temperature resistant colonies. Another method of curing cells is based on the selective killing of rapidly replicating DNA molecules by a combination of ultraviolet light and incorporation of 5- bromodeoxyuridine; b) reinfecting or transfecting cured cells or infecting noncariogenic strains with the phages or phage nucleic acid and then determining the cariogenic potential of the bacteria. The cured bacteria will be utilized as recipient cells in transformation experiments. We seek to determine the exact site of chromosomal attachment of the prophage. Mutagenic studies with nitrosoguanidine will also be extended to determine the indispensable biochemical characteristics of cariogenic streptococci. The bacteriophage that are present in different strains of cariogenic bacteria will be compared by immunological methods.